1. Field of the Invention
The present invention relates to an isolated signal transmitting device, an isolated signal transmitting circuit and a receiving circuit thereof, and especially relates to a transmitting device for separately transmitting digital signals and analog signals, wherein an input and output of the transmitting device are not commonly grounded.
2. Description of the Related Art
Multiple common power supplies that are electronically connected with each other in parallel or series are commonly grounded. Namely, when the multiple power supplies respectively supply multiple loads, the multiple loads are commonly grounded. One of the power supplies is the master power supply, and the others are slave power supplies. A user can control the master power supply to transmit control signals for controlling whether the slave power supplies supply power to the loads or not. Firstly, the user electronically connects the master power supply and the slave power supplies according to a signal transmitting circuit, and respectively sets output voltages of the slave power supplies. Then, the user electronically connects the loads with outputs of the slave power supplies, and the user can turn on or off of the slave power supplies by controlling the master power supply to determine whether the loads are powered or not.
For example, the master power supply outputs an output voltage of 15 volts to a first load, and the slave power supply outputs an output voltage of 3.3 volts to a second load. The user can simultaneously turn on the master power supply and the slave power supply to power the first load and the second load, or may turn on the master power supply firstly and turn on the slave power supply after a while, depending on demand of the user.
The master power supply and the slave power supply are commonly grounded because the signal transmitting circuit is designed according to the principle of common ground. Therefore, the outputs of the master power supply and the slave power supply are commonly grounded, and the first load and the second load have only one ground voltage. When the user needs to power multiple loads and the multiple loads cannot be commonly grounded, the signal transmitting circuit cannot be used to electronically connect the master power supply and the slave power supply. The user needs to separately and manually turn on each of the master power supply and the slave power supply, and the user cannot precisely turn on the master power supply and the slave power supply at the same time. Therefore, the signal transmitting circuit needs to be improved.